# 2024.04.21

```cpp
template <typename T>
void QWidgetPrivate::update(T r)
{
    Q_Q(QWidget);

    if (!q->isVisible() || !q->updatesEnabled())
        return;

    T clipped = r & q->rect();

    if (clipped.isEmpty())
        return;

    if (q->testAttribute(Qt::WA_WState_InPaintEvent)) {
        QApplication::postEvent(q, new QUpdateLaterEvent(clipped));
        return;
    }

    QTLWExtra *tlwExtra = q->window()->d_func()->maybeTopData();
    if (tlwExtra && !tlwExtra->inTopLevelResize && tlwExtra->backingStore)
        tlwExtra->backingStoreTracker->markDirty(clipped, q);
}
```

其中Q\_Q是一个宏，其定义位于qglobal.h文件

```cpp
#define Q_Q(Class) Class * const q = q_func()
```

所以 q 是一个指向QWidget的指针（关键问题在于是怎么指回去的）

```cpp
q->testAttribute(Qt::WA_WState_InPaintEvent)

inline bool QWidget::testAttribute(Qt::WidgetAttribute attribute) const
{
    if (attribute < int(8*sizeof(uint)))
        return data->widget_attributes & (1<<attribute);
    return testAttribute_helper(attribute);
}
```

q\_func()又是何方神圣呢？在qwidget\_p.h中，

```cpp
class Q_WIDGETS_EXPORT QWidgetPrivate : public QObjectPrivate
{
    Q_DECLARE_PUBLIC(QWidget)
}
```

其中Q\_DECLARE\_PUBLIC是一个宏，其定义位于qglobal.h文件

```cpp
#define Q_DECLARE_PUBLIC(Class)                                    \
    inline Class* q_func() { return static_cast<Class *>(q_ptr); } \
    inline const Class* q_func() const { return static_cast<const Class *>(q_ptr); } \
    friend class Class;
```

再看q\_ptr是什么，

QWidgetPrivate继承自QObjectPrivate，QObjectPrivate继承自QObjectdata


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